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International audience; Photonics have developed greatly over the last several decades and brought about a variety of new concepts in communica tions, sensing, solar energy and many other fields. With the emerging applications of quantum technologies and all optical data processing, the impact of photonics on technology is unde niable, as evidenced through the International Year of Light and Light based Technologies in 2015.

International audience; We propose to use a femtosecond direct laser writing technique to realize dielectric optical elements from photo-resist materials for the generation of structured light from purely geometrical phase transformations. This is illustrated by the fabrication and characterization of spin-to-orbital optical angular momentum couplers generating optical vortices of topological charge from 1 to 20. In addition, the technique is scalable and allows obtaining microscopic to macroscopic flat optics. These results thus demonstrate that direct 3D photopolymerization technology qualifies for the realization of spin-controlled geometric phase optical elements.

International audience; We propose a novel class of refractive optical elements by wrinkling the conical surface of a usual (conical) axicon, which leads to geometrical singularities (cusps). Such wrinkled axicons have been fabricated at the micron scale by using three-dimensional femtosecond-laser photopolymerization technique and we report on their experimental and numerical characterization. The beam shaping capabilities of these structures are discussed for both intensity and phase, which includes topological beam shaping that results from azimuthally modulated optical spin-orbit interaction.

International audience; Tailoring the spatial degree of freedom of light is an essential step towards the realization of advanced optical manipulation tools. A topical challenge consists of device miniaturization for improved performance and enhanced functionality at the micron scale. We demonstrate a novel approach that combines the additive three-dimensional (3D) structuring capability of laser polymerization and the subtractive subwavelength resolution patterning of focused ion beam lithography. As a case in point hybrid (dielectric/metallic) micro-optical elements that deliver a well-defined topological shaping of light are produced. Here we report on hybrid 3D binary spiral zone plates with unit and double topological charge. Their optical performances are compared to corresponding 2D counterparts both numerically and experimentally. Cooperative refractive capabilities without compromising topological beam shaping are shown. Realization of advanced designs where the dielectric architecture itself is endowed with singular properties is also discussed.

International audience; Submicron-thick gold fi lms endowed with subwavelength patterning allow on-demand topological shaping of light, hence the precise delivery of optical orbital angular momentum. Several kinds of metallic metasurfaces enabling the generation of optical vortices with arbitrary topological charges in the visible domain are fabricated following a design based on space-variant subwavelength grating with discrete orientational distribution. The optical performances of obtained fl at spin–orbit optical elements designed to operate at 532 nm wavelength are experimentally assessed and satisfactorily compared to expectations. About 80% of optical vortex generation purity for predetermined topological charge up to | l | = 10 is achieved. Other designs that allow continuous orientational distribution of nanogratings as well as the superposition of orbital angular momentum states are also proposed.

Focused ion beam (FIB) milling with a 10 nm resolution is used to directly write metallic metasurfaces and micro-optical elements capable to create structured light fields. Surface density of fabricated nano-features, their edge steepness as well as ion implantation extension around the cut line depend on the ion beam intensity profile. The FIB beam intensity cross section was evaluated using atomic force microscopy (AFM) scans of milled line arrays on a thin Pt film. Approximation of two Gaussian intensity distributions describes the actual beam profile composed of central high intensity part and peripheral wings. FIB fabrication reaching aspect ratio of 10 in gold film is demonstrated.

International audience; We show that micro‐explosions generated by tightly focused single pulses of a femtosecond laser in olivine have produced change of iron valence state. Chemical and structural changes were investigated using synchrotron X‐ray spectroscopy, and Raman scattering. Near edge X‐ray absorption fine structure (NEXAFS) spectra from laser‐affected zone of olivine crystal indicate a modified chemical bonding and a possible formation of regions containing a new crystalline phases of iron. Raman scattering from the laser‐affected zone regions reveals loss of crystalline order and formation of a mixture of nano‐crystallites due to melting and re‐solidification of olivine. These results indicate that spatial separation between ions of different mass occurs in hot, highly excited olivine. The present study confirms that this mechanism may present a general pathway toward creation of novel crystalline and amorphous nano‐materials using fs laser‐induced confined micro‐explosions.

International audience; We simulate the spectral properties of simple plasmonic nanoparticles (NPs), which we have fabricated with electron beam lithography (EBL) and lift-off, with or without nano-grooves milled by ion-beam lithography (IBL). We estimate the NP behaviour under laser illumination using 3D finite difference time domain (FDTD) simulations, showing that simple non-chiral NPs can generate torque from circularly polarized beams and emit optical vortices via spin-orbit coupling. We demonstrate numerically the position and intensity control of field enhancement hot-spots in chiral NPs illuminated by optical vortex, by combining spin/orbit momentum and NP chirality.

We report on the characterization of structural modifications created by micro-explosions at the beam waist of a tightly focused femtosecond laser pulse inside of GeO2 glass. Micro-Raman scattering revealed the presence of structurally strongly modified regions at and around the irradiated sites. For separations of 5 μm between adjacent irradiated sites structural modifications due to a pressure increase are observed, whereas smaller spacings of 2 μm lead to thermal effects and crystallization. The mechanisms and the interplay of pressure and temperature effects are discussed.

International audience; We propose and experimentally demonstrate a geometrical approach to the controlled generation of optical phase singularities at small scale by using metallic nanostructures, thereby offering a novel strategy towards singular nanophotonics.